Assuming an AWS STS role (with multi-factor authentication) using Ruby

assumeRole.rb

def assumeRole(region: 'eu-west-1', role_arn: nil, session: 'temp', duration: 3600, mfa_arn: nil, token: nil)
  # returns a Credentials object for the assumed role, built from:
  #   region: the AWS region to connect to (default: eu-west-1),
  #   role_arn: the role ARN that you want to assume,
  #   session: the name you want to give the session (default: 'temp'),
  #   duration: seconds the assumed role is valid for (default: 3600),
  #   mfa_arn: the ARN for the MFA token associated with the user
  #   token: the 6-digit token ID from the MFA device
  # 
  # This assumes that you have already defined your normal AWS credentials,
  # either as environment variables, or in the .aws directory.
  # 
  begin
    # Create an AWS STS Client object in the specified region
    user_client = Aws::STS::Client.new(region: region)

    # Create the assumed role credentials
    assumed_role = Aws::AssumeRoleCredentials.new(
                    client: user_client,
                    role_arn: role_arn,
                    role_session_name: session,
                    duration_seconds: duration,
                    serial_number: mfa_arn,
                    token_code: token
                    )

    # return the assumed role credentials object
    return assumed_role
    
  # Error handling
  rescue StandardError => e
    puts "Error in assumeRole: #{e.message}"
    return nil
  end
end